Field of the Invention
The present invention relates to an improved process for manufacturing bis-(hydroxyphenyl)methanes. More particularly, the present invention is related to a process with improved selectivity for a 2,4′-bis(hydroxyphenyl)methane isomer and overall improved productivity due to a low molar ratio of phenol to formaldehyde, at a high reaction temperature, workable within an atmospheric pressure range. The present invention, with its higher selectivity for 2,4′-bis-(hydroxyphenyl)methane, is useful for making some specialty non-crystallizing grades of novolak-based epoxy resins on an industrial scale.
The present process comprises reacting high purity as well as recovered phenol, containing water, from same process, with formaldehyde in presence of inorganic acidic catalyst at specific range of reaction temperatures 85-100 degree C. which favours high ortho-para isomer despite lower phenol:formaldehyde ratio leading to higher productivity & easy recyclability of spent catalyst.
Description of Prior Art
Conventional bisphenol F and novolac resins are prepared from phenolic compounds and formaldehyde in the presence of an acidic catalyst like H2SO4 or oxalic acid. Such resins may have a relatively high proportion of para-para and ortho-para methylene bridges, as illustrated below.

High ortho novolac resins are characterized by ortho/ortho methylene bridges and have a much greater speed of curing with hardeners like hexamethylene tetraamine.

4,4′-Dihydroxydiphenylmethane is useful starting material for the production of polycarbonate resins, polyester resins, and epoxy novolac resin, and as a modifier and stabilizer for phenol resins [U.S. Pat. No. 6,492,566].
To meet end application requirements, a desired blend of properties, like curing speed, reactivity, and other end properties like softening point, Tg, control of the isomer ratio between ortho-ortho, ortho-para and para-para, and the monomer:oligomer ratio becomecritical. Selection of catalyst type has a detrimental effect on the isomer ratio and overall monomer content, as well as dimer and oligomer ratios and/or proportions.
Several methods are known for preparing dihydroxydiphenylmethanes. Conventional methods comprising reacting phenol with dimethylol urea in the presence of hydrochloric acid (40% HCl) or glacial acetic acid can afford 47.9% yield of diphenylolmethane [U.S. Pat. No. 2,617,832].
JP-B-39-26844 discloses a method for reacting phenol with formaldehyde in the presence of urea, filtering the solid thus precipitated, and recrystallizing the same from water.
U.S. Pat. No. 4,400,554 discloses a method for reacting phenol with formaldehyde in the presence of aqueous H3PO4. An object of this invention is to afford a high concentration of 4,4′-isomer. Typical 4,4′-, 2,4′-, and 2,2′-dihydroxydiphenylmethanes in a ratio of 55:37:8 have been reported. The molar ratio of phenol to formaldehyde is in the range of about 3:1 to 20:1.
U.S. Pat. No. 4,937,392 discloses a process for reacting phenol with formaldehyde with catalysts such as oxalic acid and activated clay at molar ratios of phenol:formaldehyde (P:F) starting from 8 to 25. The range of individual isomers of bis-(hydroxyphenyl)methane varies from 29.5%-44.5% of the 4,4′ isomer, 40.5%-50.3% of the 2,4′ isomer, and 16.5%-20.6% of the 2,2′ isomer. An object of this invention is to get high selectivity for 4,4′-dihydroxydiphenylmethane relative to 2,4′-dihydroxydiphenylmethane.
To lower the content of oligomers, including trimers, preferred phenol:formaldehyde molar ratio can be as high as 20:1 and 25:1. However, the process has several disadvantages from an industrial point of view. For example, the process has the drawback of using a very high phenol:formaldehyde ratio, and use of a heterogeneous catalyst like clay which, from the industrial point of view, is disadvantageous since it calls for an additional unit operation like filtration.
U.S. Pat. No. 6,492,566 discloses a process for reacting phenol with formaldehyde in presence of a microporous alumino-silicate zeolite catalyst to afford a high proportion of 2,4′-dihydroxydiphenylmethane (about 46%-53%), and lower proportions of 2,2′-dihydroxydiphenylmethane (about 15%-33%) and 4,4′-dihydroxydiphenylmethane (about 13%-27%). However, the process has certain disadvantages. Although microporous zeolites can provide a high selectivity of 2,4′-dihydroxydiphenylmethane, the percent conversion is very low.
Use of a high pressure autoclave, a heterogeneous catalyst filtration step, and lower percent conversions to dihydroxydiphenylmethane (on the order of 14% to 23%), when the molar ratio of phenol to formaldehyde is between from 5:1 to 10:1, makes this process industrially unattractive.
U.S. Pat. No. 5,654,382 and WO9702306 disclose that bisphenol F containing a higher proportion of 2,2′- and 2,4′-isomers lowers the melt viscosity and solution viscosity of bisphenol F epoxy resin. However, both patents are silent on any method to increase the proportions of the 2,2′- and 2,4′-isomers of bisphenol F.
CN 102070409A discloses the preparation of bisphenol F with a high proportion of ortho isomers, but the reaction procedure involves usage of high purity molten phenol, dosing of formaldehyde in two shots at two different temperature conditions (70° C. and 60° C., respectively), and a relatively high phenol to formaldehyde ratio on the order of 12-25, which makes this process industrially unattractive. Moreover, this patent is silent on the impact of the high monomer content in general and the 2,4′-isomer specifically on the crystallization resistance properties of bisphenol F epoxy resin. Also injecting ammonia in the molten phenol before charging the phosphoric acid catalyst further adds one additional step which makes this process industrially unattractive.
In the prior art, wherever oxalic acid or phosphoric acid is used as a catalyst, to get a relatively high percentage of 2,4′-dihydroxydiphenylmethanes (e.g., >45%), a molar ratio of phenol:formaldehyde exceeding 12-25:1 is generally required, which makes the manufacturing process unattractive due to high vessel occupancy and/or volume in the reactor by the phenol, the relatively high energy cost for recovery of un-reacted phenol, and the relatively low productivity per batch from the reactor.
CN102516035A discloses a process for the preparation of bisphenol F with a high content of ortho isomer(s) and with a low phenol to formaldehyde ratio, but suffers the disadvantage of using an organic monobasic or dibasic co-catalyst with the inorganic acidic catalyst. This makes this process industrially less attractive, as recovery of the catalyst(s) from the spent acid catalyst stream is relatively complex, and usage of an organic acid as co-catalyst causes an increased load of salts in the organic stream during the neutralization step.
The use of dihydroxydiphenylmethane with a relatively high percentage of 2,4′-dihydroxydiphenylmethane and a low oligomer content is preferred as a starting material for high performance bisphenol F base epoxy resins. These epoxy resins are used for civil applications, as they have high workability and ease of transportation in cold regions due to a very low crystallization tendency. The demand for such specialty bisphenol F based epoxy resins is increasing day by day.